NAME
r.average - Finds the average of values in a cover map within
areas assigned the same category value in a user-specified base map.
(GRASS Raster Program)
SYNOPSIS
r.average
r.average help
r.average
[-c]
base=name
cover=name
output=name
DESCRIPTION
r.average calculates the average value of data
contained in a cover raster map layer for areas
assigned the same category value in the user-specified
base raster map layer. These averaged values are
stored in the category labels file associated with a new
output map layer.
The values to be averaged are taken from a user-specified
cover map. The category values for the
cover map will be averaged, unless the -c
flag is set. If the -c flag is set, the values that
appear in the category labels file for the
cover map will be averaged instead (see example
below).
The output map is actually a reclass of
the base map (see r.reclass), and will
have exactly the same category values as the
base map. The averaged values computed by
r.average are stored in the output map's
category labels file.
If the user simply types r.average on the command line, the
user is prompted for the flag setting and parameter values
through the standard
parser interface.
Alternately, the user can supply all needed flag settings and parameter values
on the command line.
Flag:
- -c
- Take the average of the values found in the
category labels for the cover map, rather
than the average of the cover map's
category values.
Parameters:
- base=name
- An existing raster map layer in the user's current
mapset search path. For each group of cells assigned the
same category value in the base map, the values
assigned these cells in the cover map will be
averaged.
- cover=name
- An existing raster map layer containing the values (in
the form of cell category values or cell category labels)
to be averaged within each category of the base
map.
- output=name
- The name of a new map layer to contain program output
(a reclass of the base map). Averaged
values will be stored in the output map's category
labels file under the user's $LOCATION/cats directory.
EXAMPLE
Assume that
farms
is a map with 7 farms (i.e., 7 categories), and that
soils.Kfactor
is a map of soil K factor values with the following category file:
cat cat
value label
0 no soil data
1 .10
2 .15
3 .17
4 .20
5 .24
6 .28
7 .32
8 .37
9 .43
Then
-
r.average -c base=farms
cover=soils.Kfactor output=K.by.farm
will compute the average soil K factor for each farm, and store the result
in the output map
K.by.farm,
which will be a reclass of
farms
with category labels as follows (example only):
cat cat
value label
1 .1023
2 .1532
3 .172
4 .3872
5 .003
6 .28
7 .2345
NOTES
The -c option requires that the category label for
each category in the cover map be a valid number,
integer, or decimal. To be exact, if the first item in the
label is numeric, then that value is used. Otherwise, zero
is used. The following table covers all possible cases:
category value
label used by -c
______________________
.12 .12
.80 KF .8
no data 0
(This flag is very similar to the @ operator in
r.mapcalc,
and the user is encouraged to read the manual entry for
r.mapcalc
to see how it works there.)
The user should use the results of r.average with
care. Since this utility assigns a value to each cell
which is based on global information (i.e., information at
spatial locations other than just the location of the cell
itself), the resultant map layer is only valid if the
geographic region and mask settings are the same as they
were at the time that the result map was created.
Results are affected by the current region settings and mask.
SEE ALSO
g.region
r.cats
r.clump
r.describe
r.mapcalc
r.mask
r.mfilter
r.mode
r.neighbors
r.reclass
r.stats
parser
AUTHOR
Michael Shapiro,
U.S. Army Construction Engineering
Research Laboratory